1. Field of the Invention
This invention relates to underground mining and more particularly to a mining machine for forming an entry in a multi-entry mine.
2. Description of the Prior Art
Longwall mining is becoming the preferred method of removing coal from a deep underground mine. Generally, longwall mining is a system for removing coal from an extended face of coal, say several hundred feet in length, as opposed to removing coal from a face that is essentially the width of a continuous mining machine.
The formation of entries in a multi-entry mine where longwall mining is carried out presents a problem in that the longwall mining apparatus can remove coal faster than the required entries can be formed. The known entry forming machines use separate pieces of machinery for removing coal from the entries and for providing the necessary roof support. For example, a continuous mining machine typically is used to drive an entry until the established limits of unsupported roof above it are reached; the mining machine is backed away from the entry face and moved to another entry for further driving while a roof bolter is moved into the entry vacated by the mining machine to install the required roof bolts. This procedure requires a large number of equipment moves and thus presents a hazard to personnel in the coal mine because the rate of equipment movement must be relatively rapid to optimize efficiency.
Furthermore, the requirement of rapid movement by separate items of equipment renders impractical the use of a mining machine for each entry, not only because of the expense involved but also because of the equipment congestion that would ensue. In addition, a conventional continuous mining machine, which is usually self-propelled on threads or the like, cannot easily be turned 90.degree. within a mine entry to form the necessary cross-cuts in a multi-entry mine system. Accordingly, in the typical multi-entry mine, only one mining machine is employed to drive say three entries; this means that the mining machine spends a considerable amount of time in transiting between entries and spends relatively little time at the entry faces removing mineral.